Our goal is to describe the neural mechanisms responsible for stabilization and shifts of gaze in cats and primates. Gaze stabilization mechanisms will be investigated by recording reflex responses and the related activity of brainstem neurons with identified input and output connections during rotation of the whole body (vestibular stimulation) and rotation of the head with respect to the body (stimulation of neck receptors). Sinusoidal rotations and linear systems analysis techniques will be used to measure reflexly induced eye and head movements and neuronal activity as a function of stimulus frequency and to determine how neck and vestibular reflexes interact with each other and with movements induced by visual stimulation. Gaze shift (saccadic) systems will be investigated by recording muscle activity, eye movements, head movements, and discharge of identified brainstem neurons during gaze shifts produced by visual stimuli or microstimulation of the superior colliculus. The variation of saccadic movements with initial eye position and their interaction with vestibular and neck reflexes will be investigated. Mechanisms responsible for recovery of accurate gaze control following loss of vestibular function will be investigated by examining plastic changes in neck reflex activity and in the amplitude of saccadic gaze shifts following vestibular lesions. We will also investigate adaptive changes in vestibular and neck reflexes induced by abnormal visual image motion. Collectively the proposed experiments should provide information about the structure and function of pathways involved in gaze control, which will be helpful in devising clinical procedures for diagnosing and alleviating gaze control disorders and which will contribute to the understanding of basic mechanisms that regulate motor behavior.